Projectile fin

ABSTRACT

The invention is a projectile stabilizing fin formed with a laterally  exting flat, triangular shaped tab positioned so that one point of the triangle points in the direction of the intended projectile direction and tilted so that air flow will impinge on the tab surface and cause the projectile to spin. Such construction is particularly useful for projectiles launched from smooth bore guns at high Kinetic Energy.

GOVERNMENTAL INTEREST

The invention described herein may be manufactured, used and licensed byor for the Government for Governmental purposes without the payment tome of any royalties thereon.

BACKGROUND OF THE INVENTION

This invention relates to a stabilizing fin used to stabilizeprojectiles or missiles launched at high muzzle velocity.

Current high length to diameter ratio missiles or projectiles such asprojectiles fired from a tank must be statically stabilized by finsprojecting from the missile body generally from its trailing end. Whensuch projectiles are fired from smooth bore guns, such fins (generally 3to 6 in number) must generate a roll or spin to the projectile byaerodynamic means. Such spin must be at a rate necessary to average outthe transverse lift due to asymmetry resulting from manufacturinginaccuracies.

Projectile fins are presently fabricated from aluminum because of itsweight and a low cost. To achieve spin such aluminum fins are typicallymechanically beveled at their leading and/or trailing edges or they arecanted to aerodynamically induce the necessary torque for the requiredspin rate.

However todays and future projectile requirements include higher impactvelocities and aluminum or aluminum base alloys fail to meet therequirements of such increased velocities because aluminum fins tend toburn or melt due to aerodynamic heating at such velocities.

SUMMARY OF THE INVENTION

It has been determined that high strength, high melting alloys such asthose of steel can be used to make such fins that do not melt or burnand which improve the aerodynamic properties of such fins. Howeverweight considerations require such fins to be substantially thinner thanaluminum alloy fins and consequently may not be beveled to effect thenecessary spin to the projectile.

The present invention is the discovery that flat triangular shaped fintabs may be provided to the outer surface or tip chord of such fins thatwill provide the necessary torque to the projectile for stabilization athigh kinetic energy (KE) velocities.

The triangular shaped tabs extend laterally from each fin pointing intothe direction of intended projectile travel and tilted in respect tosuch direction to form an angle in respect to the axis or direction oftravel of the missile. In this position the air flow pressure on thetilted tabs will effect the necessary torque on the missile to achievethe desired rotation. The exact tab dimension, position on the fin angleof tilt and uniformity on each fin will, of course, depend on the exactrequirements of the missile itself (i.e. size, velocity, application).

It is the object of this invention to provide improved stabilizing finsfor projectiles that are launched from smooth bore guns at highvelocity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a projectile fin showing the fin tabconstruction of the present invention and shown as attached to a portionof a projectile; and

FIG. 2 is a top view of the projectile fin of FIG. 1.

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific terms so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose. For example, theword connected or terms similar thereto are often used. They are notlimited to direct connection but include connection through otherelements where such connection is recognized as being equivalent bythose skilled in the art.

DETAILED DESCRIPTION

In the drawing of FIG. 1, projectile fin 2 is shown as attached to atypically cylindrically shaped projectile 4 (only a portion of which isshown). Fin 2 is itself of generally elongated flat triangular shapeextending transversely from the projectile along planes containing itsaxis with sharpest angle point 6 pointed in the direction the missile 4will travel as opposed to the direction of air flow 8. The fin tab 10 ofthe present invention as shown by FIG. 2 is also of flat triangularshape (but may be of other aerodynamic shape). Fin tab 10 is attached to(or being an integral part of) fin 2 and extends laterally from thesurface of fin 2 and one point of the tab also points into the directionthe missile 4 will travel as opposed to the direction of air flow 8.(FIG. 2)

Fin tab 10 as shown by FIG. 1 is angularly positioned in respect to theaxis 12 of projectile 4 and thus the direction of travel of the missileand the opposite direction of air flow 8.

This angle results in air pressure on the surface 14 of the fin tab 10by air flow 8 causing torque forces on the tab and spin to the missile.The exact angle tab 10 forms in respect to the intended direction of themissile (and thus opposite air flow 8) is, of course, dependent on thespin or rotation requirement of the exact missile. However, such anglewill be expected to be within the range of from about 2 degrees to 7degrees.

The embodiment of the present invention depicted by FIGS. 1 and 2 showtab 10 extending laterally at a 90 degree angle from the upper rear edgeof fin 2. The tab 10 is positioned angularly upward in respect to airflow 8 (or axis 12) and is positioned on the left hand side (lookingforward) of the fin so that the missile will spin clockwise. This is theconventional arrangement, however, obviously it may be desired to placefin tab 2 elsewhere on fin 2, on the opposite side of the fin and angleddownwardly or upwardly depending on the exact projectile to which it isapplied and the results desired. The triangular shape of fin tab 2 mayalso vary from a perfect triangle to one of greater length than thatshown by FIGS. 1 and 2 depending on the exact parameter sought.

The fin 2 of the present invention may also vary in shape but ispreferably of the shape shown by FIGS. 1 and 2.

Fin 2 and fin tab 10 of the present invention can be made with steel orany other material of higher heat resistance and strength than aluminumor aluminum base alloys.

Fin 2 and fin tab 10 is designed for a kinetic energy (KE) projectilelaunched at high supersonic muzzle velocity, especially from a smoothbore gun tube. This fin can be made with steel or any other high meltingtemperature and high strength metal such as stainless steel. With thesematerials, the fin burning due to aerodynamic heating is eliminated anda low aerodynamic drag is accomplished because of the thin fin blades.However, since the projectile is fired from a smooth bore gun tube,projectile spin rate has to be attained by aerodynamic means. The spinrate is necessary to even out the transverse lift due to asymmetryresulting from manufacturing for flight stability and accuracyrequirements. The spin rate of a KE projectile is extremely difficult,if not impossible to control by beveling a thin fin due to the expensivemanufacturing accuracy required. The small fin tab 10 is attached to thetip of each fin blade 2 to generate spin moment instead of beveling. Thesize and the tilt angle of the tab can be adjusted very easily to obtainproper spin rate to avoid resonant flight instability occurrence withthe nutational frequency of the projectile or the bending frequency ofthe penetrator (mechanical resonance).

A fin design, similar to the one shown in FIGS. 1 and 2, has beenfabricated from stainless steel by using the investment castingtechnique. This fin was 4.25 inches in length, 0.90 inches wide (at itstrailing edge) and 0.074 inches thick (at it thickest dimension). Thefin tab was 0.038 inches in thickness and was tilted at a 5 degree anglein respect to the axis of the missile. The test results from YumaProving Ground successfully proved that this type of fin design madewith the investment casting process. It survived the gun launchenvironment with the fin tabs intact. More important, the result fromthe AEDC wind tunnel test showed that this fin design did provideadequate flight stability, low drag and desired spin moment.

While certain preferred embodiments of the present invention have beendisclosed in detail, it is to be understood that various modificationsmay be adopted without departing from the spirit of the invention orscope of the following claims.

I claim:
 1. A projectile fin formed with a laterally extending flat,triangular shaped member positioned so that one point of the trianglepoints in the intended projectile direction and tilted in respect tosuch direction so that air pressure will impinge on one surface of saidmember during projectile flight to provide rotation to the projectile.2. The projectile fin of claim 1 wherein said triangular shaped memberis attached to the outermost edge of the fin.
 3. The projectile fin ofclaim 1 wherein the fin is constructed of a metal having a highermelting temperature and strength than aluminum or aluminum base alloy.4. The projectile fin of claim 1 wherein the fin is constructed ofstainless steel.
 5. The projectile fin of claim 1 wherein the flattriangular shaped member is tilted upwardly at an angle of from about 2degrees to 7 degrees in respect to the intended projectile direction. 6.A cylindrically shaped projectile formed with thin flat stabilizationfins extending transversely of said projectile and positionedequidistant to one another, each such fin having a laterally extending,flat triangular shaped member positioned so that one point of thetriangle points in the intended projectile direction and angled inrespect to such direction so that air pressure will impinge on onesurface of said member during projectile flight to provide spin to saidprojectile.
 7. The projectile of claim 6 wherein the fins areconstructed of a metal having a higher melting temperature and strengththan aluminum or aluminum base alloys.
 8. The projectile of claim 6wherein the fins are constructed of stainless steel.
 9. The projectileof claim 6 wherein the flat triangular shaped members are each tilted atan angle of from about 2 to 7 degrees in respect to the intendedprojectile direction.
 10. The projectile of claim 6 wherein the fins areconstructed of a material of higher heat resistance and strength thanaluminum or aluminum base alloys.